Definitely get two. My husband and I both work full time, and our little guys are just fine with each other all day. They don't really mind it at all when we leave, because they each get a treat when it's time to go to their crate for the day.
I don't agree with yorkieusa about not getting litter mates, though. Ours are brothers from the same litter, and they've definitely bonded to us.
Of course, they act like brothers, too - one minute they're fighting, the next minute they're best friends.